In recent years, the use of an inkjet system recording device as a recording device for outputting information to a recording medium has been widespread rapidly along with the spread of personal computers and the advancement of multimedia.
An inkjet head is mounted on the inkjet system recording device. This type of inkjet head has a pressurizing means within an ink passage filled with ink. By the pressurizing means, the ink within the ink passage is pressurized and discharged as ink droplets from an ink discharge hole. Thermal system equipped with a heater as the pressurizing means in which ink is heated and boiled by the heater, and the ink is pressurized by bubbles generated in the ink passage; and piezoelectric system equipped with a piezoelectric element as the pressurizing means in which bending displacement of part of the ink passage filled with ink is caused by the piezoelectric element, and the ink in the ink passage is mechanically pressurized are generally known.
A print head used in an inkjet recording device using the piezoelectric system has, for example, the structure as shown in FIG. 3(a) in which a plurality of grooves are arranged side by side as ink passages 23a, and an actuator 21 is disposed on a passage member 23 with a partition wall 23b formed as a wall for partitioning the individual ink passages 23a. 
The actuator 21 is made up of a plurality of displacement elements 27 by forming an internal electrode 25 on one main surface of a piezoelectric ceramic layer 24, and by forming a plurality of individual electrodes 26 on the other main surface. The actuator 21 is connected to the passage member 23 so that the individual electrodes 26 are located immediately above the ink passage 23a as an opening part of the passage member 23.
By applying a voltage between the internal electrode 25 and these individual electrodes 26, these displacement elements 27 are oscillated so that the ink within the ink passage 23a is pressurized to discharge ink droplets from an ink discharge hole 28 opening into the bottom surface of the passage member 23.
It is possible to contribute to high speed and high accuracy of inkjet printers by constructing a print head in which a large number of individual electrodes 26 are disposed side by side at equal pitches on the piezoelectric ceramic layer 24, and a large number of displacement elements 27 are disposed as shown in FIG. 3(b), and by independently controlling the individual displacement elements 27.
Patent document 1 discloses the high-endurance piezoelectric ceramics used in the above piezoelectric actuator. The piezoelectric ceramics employs, as a main crystal phase, oxide ceramics of a perovskite-type crystal structure having an average particle diameter of 1 to 8 μm and exhibiting piezoelectric, performance, and contains at least one kind of fine grains selected from Al2O3, MgO, ZrO2, AgO, Ag and Pt, each having an average grain diameter of 0.5 μm or less, in a proportion of 0.1 to 5.0% by volume. The time to reach rupture or fracture by repetitive applications of high-voltage sine-wave of 2 kV/mm and 1 kHz along the polarization direction is 100 hours or more, and 5% or more of particles in the fractured section correspond to intergranular fracture.    Patent document 1: Japanese Unexamined Patent Application Publication No. 2000-211968